The subject of this invention is an axial-centrifugal compressor having a system for controlling axial play.
An axial-centrifugal compressor comprises a first conventional portion, where the rotor and the stator are cylindrical and concentric around the axis line of the compressor, and then a portion where they spread out in a radial direction so that the corresponding portion of the rotor, called an impeller extends beyond the stator along the axis line. One of its advantages is to reduce the bulkiness of the machine in the direction of the axis and to produce more compact and more lightweight machines.
The yield of the compressors and of the machines to which they may be integrated greatly depends on the plays existing between the rotor and the stator and which are responsible for energy losses in the flow of the gases. It is conventional to adjust these plays by ventilation of a gas at the intended temperature and flow rate in order to produce differential thermal expansion between the rotor and the stator in the radial direction. Air taken from a section of the compressor is generally used in order to benefit from its pressurization and to have it circulate in conduits or cavities, towards the location where differential thermal expansion may be controlled. With a valve, it is possible to adjust the ventilation gas flow rate and the amount of heat which it provides, on the contrary draws off, according to the correction of the play required at each running speed of the machine.
The system for adjusting radial play is however applied to the stators in conventional devices. Further, these devices have only been applied to axial compressors.
There further exists ventilation devices for the rotor, in which another air flow originating from the stator crosses a radial arm supporting the rotor before penetrating into a central cavity of the latter. These ventilation devices have the only purpose of preventing excessive heating of the rotor. In particular, they are not controlled in terms of flow rate, which does not allow them to exert any play adjustment.
However mention should be made of French patent 2 698 667, wherein an axial play adjustment of an impeller of an axial-centrifugal compressor is achieved by a balance of pressure forces; of U.S. Pat. Nos. 4,687,412 and DE 21 65528 wherein the axial play is adjusted by mechanical and static means (shims or washers in bolted assemblies); and of patent FR-A-2 722 836 where it is adjusted by axial displacement, controlled by a servo-controlled actuator of the abutment bearing of the rotor.